Liquid crystal display device

ABSTRACT

An object of the invention is to repair a drain signal line easily. Each region enclosed by two gate signal lines adjacent to each other and two drain signal lines adjacent to each other that are formed on the liquid-crystal-side surface of one of transparent substrates that are opposed to each other with a liquid crystal interposed in between is made a pixel region. Each pixel region is provided with a switching element that is driven being supplied with a scanning signal from one of the two gate signal lines and a pixel electrode that is supplied, via the switching element, with a video signal from one of the two drain signal lines. A repair conductive layer is formed so as to be contained in each drain signal line when viewed perpendicularly with an insulating film interposed in between.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a liquid crystal display deviceand, in particular, to an active matrix liquid crystal display device.

[0003] 2. Description of the Related Art

[0004] In active matrix liquid crystal display devices, each of regionsthat are formed on the liquid-crystal-side surface of one of transparentsubstrates opposed to each other with a liquid crystal interposed inbetween and that are enclosed by gate signal lines extending in the xdirection and arranged in the y direction and drain signal linesextending in the y direction and arranged in the x direction is made apixel region. Each pixel region is provided with a thin-film transistorthat is driven being supplied with a scanning signal from one of thegate signal lines that define the pixel region and a pixel electrodethat is supplied, via the thin-film transistor, with a video signal fromone of the drain signal lines that define the pixel region.

[0005] Each of the above signal lines, thin-film transistors, pixelelectrodes, etc. is formed by laying one on another a conductive layer,a semiconductor layer, and an insulating layer each of which is formedin a prescribed pattern by selective etching according to aphotolithography technique.

[0006] As for recent high-resolution liquid crystal display devices, aproblem of signal line disconnection is pointed out that occursoccasionally due to small signal line widths.

[0007] A technique for solving such a problem is disclosed in JapanesePatent Laid-Open No. 19294/1993. This technique prevents what is calleda line defect that is caused by disconnection of a source signal line byforming, in each pixel, an electrical path of a source electrode (of athin-film transistor)→a gate electrode (of the thin-film transistor)→adrain electrode (of the thin-film transistor)→a pixel electrode→a firstconductor piece→a second conductor piece→a drain signal line by applyinglaser light to five locations, for example.

[0008] However, requiring two or more times of laser light applicationto repair a drain signal line, this technique has a problem that suchwork is cumbersome.

[0009] Since the first conductor piece and the second conductor pieceneed to be formed in each pixel region, this technique has anotherproblem that the aperture ratio is lowered.

[0010] This technique has a further problem that point defects (pixeldefects) are unavoidable though it can prevent line defects.

SUMMARY OF THE INVENTION

[0011] The present invention has been made in view of the abovecircumstances in the art, and an object of the invention is therefore toprovide a liquid crystal display device in which a drain line can berepaired easily.

[0012] Another object of the invention is to provide a liquid crystaldisplay device that does not obstruct increase of the pixel apertureratio.

[0013] A further object of the invention is to provide a liquid crystaldisplay device in which a point defect, not to mention a line defect,does not occur.

[0014] A typical aspect of the invention will be briefly summarizedbelow.

[0015] Each region enclosed by two gate signal lines adjacent to eachother and two drain signal lines adjacent to each other that are formedon the liquid-crystal-side surface of one of substrates that are opposedto each other with a liquid crystal interposed in between is made apixel region. Each pixel region is provided with a switching elementthat is driven being supplied with a scanning signal from one of the twogate signal lines and a pixel electrode that is supplied, via theswitching element, with a video signal from one of the two drain signallines. A repair conductive layer is formed so as to be contained in eachdrain signal line when viewed perpendicularly with an insulating filminterposed in between.

[0016] In the liquid crystal display device having the aboveconfiguration, when a disconnection occurs in a drain signal line, laserlight is applied to two locations of the disconnected drain signal lineon both sides of the disconnected portion, whereby the parts of thedrain signal line on both side of the disconnected portion are connectedto each other via the repair conductive film, that is, the disconnecteddrain signal line is repaired. This is done by only two applications oflaser light.

[0017] Since each repair conductive layer is formed so as to becontained in the associated drain signal line when viewedperpendicularly, it does not prevent increase of the pixel apertureratio.

[0018] Further, a disconnected drain line is repaired by not using amember located in a pixel region, the repairing does not cause any pixeldefect,

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a plan view of one pixel of a liquid crystal displaydevice according to a first embodiment of the present invention;

[0020]

[0021]FIG. 2 is an equivalent circuit diagram of the liquid crystaldisplay device according to the first embodiment of the invention;

[0022]

[0023]FIG. 3 is a sectional view taken along line III-III in FIG. 1;

[0024]FIG. 4 is a sectional view taken along line IV-IV in FIG. 1;

[0025]FIG. 5 illustrates an advantage of the liquid crystal displaydevice according to the first embodiment of the invention;

[0026]FIG. 6 is a sectional view taken along line VI-VI in FIG. 5;

[0027]FIG. 7A is a plan view of one pixel of a liquid crystal displaydevice according to a second embodiment of the present invention;

[0028]FIG. 7B is a sectional view taken along line b-b in FIG. 7A; and

[0029]FIG. 8 is a plan view of one pixel of a liquid crystal displaydevice according to a third embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Liquid crystal display devices according to embodiments of thepresent invention will be hereinafter described.

[0031] Embodiment 1

[0032] <Equivalent circuit>

[0033]FIG. 2 is an equivalent circuit diagram of a liquid crystaldisplay device according to a first embodiment of the invention.Although FIG. 2 is a circuit diagram, it is so drawn as to correspond toan actual geometrical arrangement.

[0034] As shown in FIG. 2, a transparent substrate SUB1 is opposed tothe other transparent substrate SUB2 with a liquid crystal interposed inbetween.

[0035] Gate signal lines GL extending in the x direction and arranged inthe y direction in FIG. 2 and drain signal lines DL extending in the ydirection and arranged in the x direction in FIG. 2 are formed on theliquid-crystal-side surface of the transparent substrate SUB1. The drainsignal lines DL are insulated from the gate signal lines GL. Each of therectangular regions enclosed by the gate lines GL and the drain lines DLis made a pixel region. A display area AR is a collection of the pixelregions.

[0036] Each pixel region is provided with a thin-film transistor TFTthat is driven being supplied with a scanning signal (voltage) from oneof the gate signal lines GL that define the pixel region and a pixelelectrode PIX that is supplied, via the thin-film transistor TFT, with avideo signal (voltage) from a one of the drain signal lines DL thatdefine the pixel region.

[0037] A capacitance element Cadd is formed between the pixel electrodePIX and the other of the gate signal lines GL that define the pixelregion. The capacitance element Cadd serves to store, for a long time, avideo signal that was supplied to the pixel electrode PIX even after thethin-film transistor TFT is turned off.

[0038] An electric field is generated between the pixel electrode PIXformed in each pixel region and a counter electrode CT (not shown) thatis formed on the liquid-crystal-side surface of the transparentsubstrate SUB2 so as to be common to all the pixel regions. The lighttransmittance of a liquid crystal portion interposed between the pixelelectrode PIX and the counter electrode CT is controlled in this manner.

[0039] Each gate signal line GL extends to one side (left side in FIG.2) of the transparent electrode SUB1, and a terminal portion GTM that isconnected to a bump of a semiconductor integrated circuit GDRC that is avertical scanning circuit mounted on the transparent substrate SUB1 isformed at the end of the extension of the gate signal line GL. Eachdrain signal line DL extends to one side (top side in FIG. 2) of thetransparent substrate SUB1, and a terminal portion DTM that is connectedto a semiconductor integrated circuit DDRC that is a video signal drivercircuit mounted on the transparent substrate SUB1 is formed at the endof the extension of the drain signal line DL.

[0040] The semiconductor integrated circuits GDRC and DDRC themselvesare completely mounted on the transparent substrate SUB1. This is whatis called a COG (chip on glass) scheme.

[0041] The input-side bumps of the semiconductor integrated circuitsGDRC and DDRC are connected to respective terminal portions GTM2 andDTM2 that are formed on the transparent substrate SUB1. The terminalportions GTM2 and DTM2 are connected, via wiring layers, to terminalportions GTM3 and DTM3, respectively, that are arranged in peripheralregions closest to the end faces of the transparent substrate SUB1.

[0042] The transparent substrate SUB2 is opposed to the transparentsubstrate SUB1 excluding the regions where the semiconductor integratedcircuits GDRC and DDRC are formed, and hence the transparent substrateSUB2 has a smaller area than the transparent substrate SUB1.

[0043] The transparent substrate SUB2 is fixed to the transparentsubstrate SUB1 with a sealing member SL that is formed in a peripheralregion of the transparent substrate SUB2. The sealing member SL also hasa function of sealing the liquid crystal that is interposed between thetransparent substrates SUB1 and SUB2.

[0044] <Pixel structure>

[0045]FIG. 1 is a plan view showing the structure of one pixel formed onthe transparent substrate SUB1 and corresponds to part A enclosed by abroken line in FIG. 2.

[0046]FIG. 3 is a sectional view (including the substrate SUB2) takenalong line III-III in FIG. 1. FIG. 4 is a sectional view taken alongline IV-IV in FIG.1.

[0047] As shown in FIG. 1, Gate signal lines GL are formed on theliquid-crystal-side surface of the transparent substrate SUB1 so as toextend in the x direction and arranged in the y direction.

[0048] Repair conductive layers RST, which were formed at the same timeas the gate signal lines GL, are formed under drain signal lines DL(described later).

[0049] The repair conductive layers RST are physically isolated andhence electrically insulated from the gate signal lines GL.

[0050] An insulating film GI made of SiN, for example, is formed on thetransparent substrate SUB1 so as to cover the gate signal lines GL andthe repair conductive layers RST (see FIGS. 3 and 4).

[0051] The insulating film GI serves, for drain signal lines DL(described later), as an interlayer insulating film for insulation fromthe gate signal lines GL, as a gate insulating film of a thin-filmtransistor TFT (described later), and as a dielectric film of acapacitance element Cadd (described later).

[0052] An i-type (intrinsic; not doped with any conductivity typedetermining impurity) semiconductor layer AS made of a-Si, for example,is formed over the associated gate signal line GL in a bottom-leftportion of each pixel region.

[0053] With a source electrode and a drain electrode formed thereon, thesemiconductor layer AS serves as the semiconductor layer of a MISthin-film transistor TFT having part of the associated gate signal lineas a gate electrode.

[0054] A source electrode SD1 and a drain electrode SD2 of the thin-filmtransistor TFT were formed at the same time as drain signal lines DLthat are formed on the insulating film GI.

[0055] The drain signal lines DL extend in the y direction and arearranged in the x direction in FIG. 1. The drain signal lines DL areformed over the repair conductive layers RST excluding regions where thegate signal lines GL are formed and their vicinities.

[0056] Part of each drain signal line DL extends so as to be locatedover the associated semiconductor layer AS and the extension serves asthe drain electrode SD2 of the associated thin-film transistor TFT.

[0057] An electrode that was formed at the same time as the drain signallines DL so as to be separated from the drain electrode SD2 is thesource electrode SD1. The source electrode SD1 is connected to a pixelelectrode PIX (described later). To secure a portion to be connected tothe pixel electrode PIX, the source electrode SD1 has a small extensionthat extends to the pixel region.

[0058] A semiconductor layer doped with an impurity is formed betweenthe semiconductor layer AS and each of the drain electrode SD2 and thesource electrode SD1, and serves as a contact layer.

[0059] The above structure can be formed in the following manner. Afterthe semiconductor layer AS is formed, a thin semiconductor layer that isdoped with an impurity is formed on the surface of the semiconductorlayer AS. Then, after the drain electrode SD2 and the source electrodeSD1 are formed, the exposed parts of the impurity-doped semiconductorlayer are etched away with the drain electrode SD2 and the sourceelectrode SD1 used as a mask.

[0060] A passivation film PSV made of SiN, for example, is formed on thetransparent substrate SUB1 (on which the drain signal lines DL plus thedrain electrodes SD2 and the source electrodes SD1) are formed) so as tocover the drain signal lines DL etc. (see FIGS. 3 and 4).

[0061] The passivation film PSV is formed to prevent direct contact ofthe thin-film transistors TFT to the liquid crystal and other purposes.The passivation film PSV is formed with contact holes CH for exposingpart of the extension of the source electrode SD 1 of each thin-filmtransistor TFT.

[0062] A transparent pixel electrode PIX made of ITO film (indium tinoxide), for example, is formed on the top surface of the passivationfilm PSV so as to cover most of the associated pixel region.

[0063] The pixel electrode PIX is formed so as to fill in the associatedcontact hole CH that is formed through the passivation film PSV, wherebythe pixel electrode PIX is connected to the source electrode SD1 of theassociated thin-film transistor TFT.

[0064] An alignment layer ORI1 is formed on the transparent substrateSUB1 (on which the pixel electrodes PIX are formed) so as to also coverthe pixel electrodes PIX. The alignment layer ORI1 is made of a resin,for example, and its surface was rubbed in a prescribed direction. Thealignment layer ORI1 is in contact with a liquid crystal LC, and theinitial alignment direction of the liquid crystal LC is determined bythe alignment layer ORI1 and another alignment layer ORI2 (describedlater).

[0065] A polarizer POL1 is attached to the surface of the transparentsubstrate SUB1 on the side opposite to the liquid crystal LC.

[0066] On the other hand, a black matrix BM is formed on theliquid-crystal-side surface of the transparent substrate SUB2 so as todefine the individual pixel regions.

[0067] The black matrix BM is provided to prevent incidence of externallight on the thin-film transistors TFT and to increase the displaycontrast.

[0068] Color filters FIL having colors corresponding to the respectivekinds of pixel regions are formed in the respective apertures (i.e.,light transmission regions that are substantially pixel regions) of theblack matrix BM.

[0069] For example, color filters FIL of the same color are used forpixel regions that are arranged in the y direction and color filters FILof red (R), green (G), and blue (B) are arranged periodically for pixelregions that are arranged in the x direction.

[0070] To prevent steps from appearing on the surface due to the blackmatrix BM and the color filters FIL, a planarization film OC, which is aresin film applied, for example, is formed on the transparent substrateSUB2 (on which the black matrix BM and the color filters FIL are formed)so as to cover the black matrix BM etc.

[0071] A counter electrode CT made of ITO, for example, is formed on thesurface of the planarization film OC so as to be common to the pixelregions.

[0072] An electric field corresponding to a video signal (voltage) isgenerated between the counter electrode CT and the pixel electrode PIXin each pixel region is used to control the alignment direction of thepart of the liquid crystal LC interposed between the above electrodes.The light transmittance is controlled by properly combining the liquidcrystal alignment direction, the above-mentioned polarizer POL1, andanother polarizer POL2 (described later).

[0073] An alignment layer ORI2 is formed on the transparent substrateSUB2 (on which the counter electrode CT is formed) so as to cover thecounter electrode CT. The alignment layer ORI2 is made of a resin, forexample, and its surface was rubbed in a prescribed direction. Thealignment layer ORI2 is in contact with the liquid crystal LC, and theinitial alignment direction of the liquid crystal LC is determined bythe alignment layers ORI1 and ORI2.

[0074] A polarizer POL2 is attached to the surface of the transparentsubstrate SUB2 on the side opposite to the liquid crystal LC.

[0075] In the liquid crystal display device having the aboveconfiguration, if a drain signal line DL is disconnected at a certainposition as shown in FIG. 5, laser light is applied to two locations ofthe drain signal line DL on both sides of the disconnected portion.

[0076] As a result, melting portions a occur in the laser-light-appliedlocations of the drain signal line DL so as to penetrate the underlyinginsulating film GI and reach the repair conductive layer RST (see FIG. 6taken along line VI-VI in FIG. 5).

[0077] The parts of the drain signal line DL that are located above andbelow the disconnected portion (as viewed in FIG. 5) are electricallyconnected to each other via the repair conductive layer RST and hencethe disconnected drain signal line DL is repaired.

[0078] As is apparent from the above description, repair of onedisconnection can be attained by two applications of laser light,providing an advantage that the repair work is easy.

[0079] Since the repair conductive layers RST are formed under the drainsignal lines DL, they do not prevent increase of the pixel apertureratio.

[0080] Further, since a drain line DL is repaired by not using a member(e.g., the pixel electrode PIX) located in a pixel region, the repairingdoes not cause any pixel defect.

[0081] Embodiment 2

[0082]FIGS. 7A and 7B show the structure of one pixel of a liquidcrystal display device according to a second embodiment of theinvention. FIG. 7A is a plan view and FIG. 7B is a sectional view takenalong line b-b in FIG. 7A.

[0083] The parts in FIGS. 7A and 7B that are given the same referencesymbols as the corresponding parts in FIGS. 1, 3, and 4 are made of thesame material and have the same function as the latter.

[0084] A first difference between the structure of FIGS. 7A and 7B andthat of FIGS. 1, 3, and 4 is that semiconductor layers AS are formedimmediately under the drain signal lines DL that are formed on theinsulating film GI.

[0085] The above semiconductor layers AS are formed at the same time asthe semiconductor layer AS of each thin film transistor TFT. Like theinsulating film GI, the semiconductor layers AS under the drain signallines DL are given a function of interlayer insulating films providedbetween the drain signal lines DL and the gate signal lines GL. It isintended to strength the interlayer insulation function.

[0086] Also in this embodiment, as in the case of the structure of FIGS.1, 3 and 4, the repair conductive layers RST are formed under the drainsignal lines DL in the layer under the insulating film GI.

[0087] Light shield films IL are formed on both sides of each drainsignal line DL, that is, on both sides of each repair conductive layerRST. Like the black matrix BM that is formed on the transparentsubstrate SUB2, the light shield films IL has a light shield function.The presence of the light shield films IL makes it possible to decreasethe width of the black matrix BM and to thereby provide an advantage ofincreasing the aperture ratio.

[0088] The light shield films IL can be formed at the same time as therepair conductive layers RST. This provides an advantage that electricalinsulation can be attained by separating the light shield films IL fromthe associated repair conductive layers RST by a prescribed distance.

[0089] If the light shield films IL were electrically connected to theassociated repair conductive layer RST, the light shield films IL wouldbe connected to the associated drain signal line DL after its repairing.This would cause adverse effects on the pixel electrodes PIX thatoverlap with the respective light shield films IL.

[0090] Embodiment 3

[0091] Each of the first and second embodiments are directed to what iscalled a vertical electric field type pixel structure. However, it goeswithout saying that the invention is not limited to such a case and canbe applied to a lateral electric field type one.

[0092] In lateral electric field type liquid crystal display devices,the structure of each drain signal line GL and its vicinity that isapproximately the same as shown in FIG. 1 is employed in the invention,because conventional lateral electric field type liquid crystal displaydevices also have the above-described problems.

[0093]FIG. 8 is a plan view showing the structure of one pixel of alateral electric field type liquid crystal display device according to athird embodiment of the invention.

[0094] In this liquid crystal display device, counter electrodes CT areformed on the liquid-crystal-side surface of a transparent substrateSUB1 (on which pixel electrodes PX are formed). The counter electrodesCT and the pixel electrodes PX are formed alternately in stripe patterns(extending in the y direction in FIG. 8).

[0095] The counter electrodes CT and the pixel electrodes PX are formedin different layers with an insulating film interposed in between. Thecomponents approximately parallel with the transparent substrate SUB1 ofelectric fields generated between the counter electrodes CT and thepixel electrodes PX are used to control the light transmittance of theliquid crystal.

[0096] The reason why each electrode has a plurality of bending portionsin its extending direction is employment of what is called a multidomainscheme in which to prevent a hue variation that would otherwise occurwhen the display screen is observed from different directions, two kindsof regions are formed where the directions of an electric fielddeveloping between a pixel electrode PX and a counter electrode CT aredifferent from each other.

[0097] As is apparent from the above description, a drain signal linecan be repaired easily in the liquid crystal display device according tothe invention.

What is claimed is:
 1. A liquid crystal display device comprising: aliquid crystal; and two substrates opposed to each other with the liquidcrystal interposed in between, the liquid crystal display device furthercomprising on a liquid-crystal-side surface of one of the twosubstrates: a plurality of gate signal lines; a plurality of drainsignal lines that cross the plurality of gate signal lines; pixelregions each enclosed by two gate signal lines adjacent to each otherand two drain signal lines adjacent to each other; a switching elementthat is provided in each pixel region and driven by a scanning signalsupplied from one of the two gate signal lines that define the pixelregion; a pixel electrode that is provided in each pixel region andsupplied, via the associated switching element, with a video signal fromone of the two drain signal lines that define the pixel region; aninsulating film; and a repair conductive layer formed so as to becontained in each of the plurality of drain signal lines when viewedperpendicularly with the insulating film interposed in between.
 2. Aliquid crystal display device according to claim 1, wherein at least oneof the plurality of drain signal lines has a disconnected portion andmelt-formed portions that are located on both sides of the disconnectedportion and penetrate the insulating film.
 3. A liquid crystal displaydevice according to claim 2, wherein the melt-formed portions of the atleast one drain signal line was formed by melting corresponding portionsof the at least one drain signal line by applying laser light to thoseportions.
 4. A liquid crystal display device comprising: a liquidcrystal; and two substrates opposed to each other with the liquidcrystal interposed in between, the liquid crystal display device furthercomprising on a liquid-crystal-side surface of one of the twosubstrates: an insulating film; a plurality of gate signal lines formedat a position closer to the one substrate than the insulating film is; aplurality of drain signal lines that cross the plurality of gate signallines and are formed at a position closer to the liquid crystal than theinsulating film is; pixel regions each enclosed by two gate signal linesadjacent to each other and two drain signal lines adjacent to eachother; a thin-film transistor that is provided in each pixel region anddriven by a scanning signal supplied from one of the two gate signallines that define the pixel region; a pixel electrode that is providedin each pixel region and supplied, via the associated thin-filmtransistor, with a video signal from one of the two drain signal linesthat define the pixel region; and a repair conductive layer formed at aposition closer to the one substrate than the insulating film is so asto be contained in each of the plurality of drain signal lines whenviewed perpendicularly.
 5. A liquid crystal display device according toclaim 4, wherein the repair conductive layer is formed in the same layerand with the same material as the plurality of gate signal lines so asto be physically separated from gate signal lines adjacent to the repairconductive layer.
 6. A liquid crystal display device comprising: aliquid crystal; and two substrates opposed to each other with the liquidcrystal interposed in between, the liquid crystal display device furthercomprising on a liquid-crystal-side surface of one of the twosubstrates: an insulating film; a plurality of gate signal lines formedat a position closer to the one substrate than the insulating film is; aplurality of drain signal lines that cross the plurality of gate signallines and are formed at a position closer to the liquid crystal than theinsulating film is; pixel regions each enclosed by two gate signal linesadjacent to each other and two drain signal lines adjacent to eachother; a thin-film transistor that is provided in each pixel region anddriven by a scanning signal supplied from one of the two gate signallines that define the pixel region; a pixel electrode that is providedin each pixel region and supplied, via the associated thin-filmtransistor, with a video signal from one of the two drain signal linesthat define the pixel region; and a repair conductive layer formed at aposition closer to the one substrate than the insulating film is so asto be contained in each of the plurality of drain signal lines whenviewed perpendicularly, at least one of the plurality of drain signallines having a disconnected portion and melt-formed portions that arelocated on both sides of the disconnected portion and penetrate theinsulating film.
 7. A liquid crystal display device according to claim6, wherein the melt-formed portions of the at least one drain signalline was formed by melting corresponding portions of the at least onedrain signal line by applying laser light to those portions.